Electro-optical displays utilizing an electro-optical material whose ability to block or transmit light is dependent on its ability to re-orient the direction of its molecular structure with respect to the direction of incident light as a result of its being converted from electrically energized state to an electrically un-energized state or vice versa is well known in the art.
Such displays typically feature the electro-optical material hermetically sealed within a cavity between two plates of which at least one of the plates is made from a transparent material such as glass or quartz or other suitable material. In instances where both of the plates are transparent, the display is termed a "transmissive type" display. In transmissive type displays, light is able to enter into the cavity through one of the plates and exit from the cavity through the other plate. A "reflective type" display on the other hand is provided where either both of the plates are transparent and a reflector is disposed on the side of one of the plates facing away from the cavity such that the reflector is able to reflect light back into the cavity that has entered into the cavity through the other transparent plate or alternatively where one of the plates is itself a non-transparent reflector able to reflect light back into the cavity that has entered into the cavity through the other transparent plate.
Electro-optical materials suitable for use in transmissive and reflective type displays are well known in the art and generally feature an organic crystalline structure alone or in combination with an organic amorphic medium with the crystalline structure having the ability to block or transmit light dependent upon the direction that incident light impinges upon the structure in combination with having the ability to re-orient the direction of its crystalline structure in response to an electrical field imposed thereacross and thus changing the direction of its crystalline structure with respect to the direction of the incident light. Electro-optical materials generally include materials such as liquid crystalline nematic materials, smectic materials and cholesteric materials in which in the absence of an electrical field, nematic materials feature the crystalline structure randomly dispersed throughout the amorphic medium, smectic materials feature the crystalline structure tending to lay in planes within the amorphic medium and cholesteric materials feature the crystalline structure in the form of coils within the amorphic medium. Most commonly in use are nematic liquid crystalline materials which preferably have sufficient positive dielectric anistrophy such that in the absence of an electrical field they tend to align substantially parallel to uni-directional rubbing lines provided by rubbing a suitable surfactant coating disposed on the surface of the plates in contact with the nematic liquid crystalline material and to align parallel to an electrical field imparted thereacross in the presence of an electrical field. Such displays become even more effective by rotating the direction of the rubbing lines on one of the plates from the direction of the rubbing lines on the other plate so as to impart a twist to the nematic liquid crystalline material and thereby increase the responsiveness of the nematic material to lower level electrical fields. Also in common use are cholesteric materials particularly when they are able to change to a nematic phase material in the presence of an electrical field. In addition, electro-optical materials commonly employ blends of two or more of liquid crystalline materials as well as blends of such materials with homologous nonliquid crystalline materials and other compatible materials such as dichroic dyes and the like to produce a particularly desired effect.
In addition to the previously described electro-optical materials, such displays may further include polarizing films disposed on one or both of the sides of the plates facing away from the cavity where desired which may be aligned or crossed to each other depending on the particular optical characteristics desired.
The electro-optical material contained within the previously described displays is commonly electrically energized by means of supplying electrical power to a transparent electrically conductive coating such as a coating of tin oxide or indium oxide disposed in the form of discrete images on the side of the plates facing toward the cavity and in contact with the electro-optical material such that, by selectively energizing the electro-optical material between a particular discrete image aligned between the plates, the electro-optical material contained in the cavity therebetween is caused to re-orient the direction of its molecular structure with respect to the direction of incident light so as to either block or transmit the image to a viewer of the display.
Although electro-optical displays have been used for many years, a problem has existed, particularly with respect to larger displays, in providing support and maintaining parallelism between the plates across the display cavity. It has been observed that undesirable refraction patterns tend to appear in the electro-optical material in regions of the cavity where the plates are closer together due to the difficultly in maintaining parallelism between the plates across the cavity and that such refraction patterns tend to become more of a problem as the size of the display cavity is increased due to the even greater difficultly in maintaining parallelism between the plates of larger displays.
Although the hermetic seal itself is generally able to provide support and maintain suitable parallelism for displays having smaller cavities, the ability of the seal to provide such support and parallelism between the plates is highly dependant upon the uniformity of pressure exerted on the seal when the plates are pressed together during the process of making the display.
As a means of aiding the seal in providing support and maintaining parallelism between the plates, it has been common practice in the past to mix solid materials such as glass beads or fibers to the electro-optical material provided that such materials are compatible with the electro-optical material and are able to be used without interfering with the electrical properties of the display and the optical properties desired of the electro-optical material. Although the addition of such materials as glass beads and fibers has been used to advantage, the practice has not been altogether satisfactory in that such materials may tend to migrate within the electro-optical material to the extent that higher concentrations occur in some regions of the cavity versus other regions and thereby diminish the ability of such materials to maintain parallelism between the plates.
More recently a support member made from glass or a flurocarbon based bead, such as disclosed in U.S. Pat. No. 3,990,781, has been disposed within the cavity such that it extends across the cavity from one plate to the other plate to provide support and maintain parallelism between the plates. Even more recently, a plurality of graphically shaped support members have been found to provide support and improve parallelism between the plates in addition to providing information to a viewer of the display regardless of whether the electro-optical material is in an electrically energized or electically un-energized state.
Although such support members within the cavity, either singularly or in conjunction with materials such as glass beads or fibers, are able to provide support and improved parallelism between the plates, a problem (as in the case with the seal above) has existed in being able to press the plates uniformly together while pressing with substantially equal force upon the hermetic sealant and upon the individual support members in order to insure that the plates are evenly spaced across the cavity so as to preclude the development of the previously described undesirable refraction patterns in the electro-optical material and thereby improve the optical uniformity of the display.